Static electric charges exceeding sparking potential and easily reaching 10kv and more are often created by engagement between different materials as a person moves about, especially in the relatively low-humidity environment inside buildings in the wintertime. The movement of footwear across a rug or movement between clothing and upholstery can easily build up an electrostatic charge that produces an electric spark when the person touches a grounded object. The sparks can exceed 1mm in length and can be painful and annoying, even though they draw little current.
Prior art solutions have included electrically conductive shoe bottoms, particularly compositions containing high percentages of conductive carbon particles. These are unsatisfactory for general use, because they abrade easily, leaving black marks, and they are safety hazards by offering a low resistance path to ground through the body of the wearer, who may be exposed to 110v or 220v from a defective household appliance. Also, conductive shoe bottoms must be worn on a conductive surface to be effective, and they are usually limited to potentially explosive environments.
Another prior art solution is antistatic materials applied to the surfaces of carpet fibers. Unfortunately, the materials used are generally ionic and depend upon ambient moisture to provide surface conductivity so they are generally unsatisfactory when relative humidity drops below 20%-25%, as frequently occurs indoors in winter. Also, these materials can only discharge the carpet fibers, and cannot discharge a person walking over the carpet.
Another potential solution is to make shoe bottoms of materials triboelectrically close enough to the floor covering to avoid electrostatic buildup. However, the wide varieties of floor coverings makes this unworkable. Finally, the surest way to avoid the shock from a spark is to moisten the hand and touch a wall, or use a coin or key to touch a grounded object, but this requires considerable forethought.
The prior art is well explained in an article entitled "Static Electricity in Textiles", by K. W. Mieszkis, and a copy is enclosed with this application. The article not only describes prior art attempts to solve the problem, but points out that the static electric potentials built up on the wearer are prodigious and readily reach thousands of volts. The hazards and annoyances of static electric charges are also evaluated in other technical literature.
The invention aims at a solution to the problem in the form of footwear that automatically prevents buildup of an electrostatic charge on the wearer, and the invention also seeks economy and simplicity in making footwear that prevents the build-up of an electrostatic charge.